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<a name="STRUCTURE-and-RECORD-1"></a>
<h4 class="subsection">5.1.22 <code>STRUCTURE</code> and <code>RECORD</code></h4>
<a name="index-STRUCTURE"></a>
<a name="index-RECORD"></a>

<p>Record structures are a pre-Fortran-90 vendor extension to create
user-defined aggregate data types.  Support for record structures in GNU
Fortran can be enabled with the <samp>-fdec-structure</samp> compile flag.
If you have a choice, you should instead use Fortran 90&rsquo;s &ldquo;derived types&rdquo;,
which have a different syntax.
</p>
<p>In many cases, record structures can easily be converted to derived types.
To convert, replace <code>STRUCTURE /</code><var>structure-name</var><code>/</code>
by <code>TYPE</code> <var>type-name</var>.  Additionally, replace
<code>RECORD /</code><var>structure-name</var><code>/</code> by
<code>TYPE(</code><var>type-name</var><code>)</code>. Finally, in the component access,
replace the period (<code>.</code>) by the percent sign (<code>%</code>).
</p>
<p>Here is an example of code using the non portable record structure syntax:
</p>
<div class="example">
<pre class="example">! Declaring a structure named ``item'' and containing three fields:
! an integer ID, an description string and a floating-point price.
STRUCTURE /item/
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END STRUCTURE

! Define two variables, an single record of type ``item''
! named ``pear'', and an array of items named ``store_catalog''
RECORD /item/ pear, store_catalog(100)

! We can directly access the fields of both variables
pear.id = 92316
pear.description = &quot;juicy D'Anjou pear&quot;
pear.price = 0.15
store_catalog(7).id = 7831
store_catalog(7).description = &quot;milk bottle&quot;
store_catalog(7).price = 1.2

! We can also manipulate the whole structure
store_catalog(12) = pear
print *, store_catalog(12)
</pre></div>

<p>This code can easily be rewritten in the Fortran 90 syntax as following:
</p>
<div class="example">
<pre class="example">! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
! ``TYPE name ... END TYPE''
TYPE item
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END TYPE

! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
TYPE(item) pear, store_catalog(100)

! Instead of using a dot (.) to access fields of a record, the
! standard syntax uses a percent sign (%)
pear%id = 92316
pear%description = &quot;juicy D'Anjou pear&quot;
pear%price = 0.15
store_catalog(7)%id = 7831
store_catalog(7)%description = &quot;milk bottle&quot;
store_catalog(7)%price = 1.2

! Assignments of a whole variable do not change
store_catalog(12) = pear
print *, store_catalog(12)
</pre></div>

<p>GNU Fortran implements STRUCTURES like derived types with the following
rules and exceptions:
</p>
<ul>
<li> Structures act like derived types with the <code>SEQUENCE</code> attribute.
Otherwise they may contain no specifiers.

</li><li> Structures may contain a special field with the name <code>%FILL</code>.
This will create an anonymous component which cannot be accessed but occupies
space just as if a component of the same type was declared in its place, useful
for alignment purposes.  As an example, the following structure will consist
of at least sixteen bytes:

<div class="smallexample">
<pre class="smallexample">structure /padded/
  character(4) start
  character(8) %FILL
  character(4) end
end structure
</pre></div>

</li><li> Structures may share names with other symbols. For example, the following
is invalid for derived types, but valid for structures:

<div class="smallexample">
<pre class="smallexample">structure /header/
  ! ...
end structure
record /header/ header
</pre></div>

</li><li> Structure types may be declared nested within another parent structure.
The syntax is:
<div class="smallexample">
<pre class="smallexample">structure /type-name/
    ...
    structure [/&lt;type-name&gt;/] &lt;field-list&gt;
...
</pre></div>

<p>The type name may be ommitted, in which case the structure type itself is
anonymous, and other structures of the same type cannot be instantiated. The
following shows some examples:
</p>
<div class="example">
<pre class="example">structure /appointment/
  ! nested structure definition: app_time is an array of two 'time'
  structure /time/ app_time (2)
    integer(1) hour, minute
  end structure
  character(10) memo
end structure

! The 'time' structure is still usable
record /time/ now
now = time(5, 30)

...

structure /appointment/
  ! anonymous nested structure definition
  structure start, end
    integer(1) hour, minute
  end structure
  character(10) memo
end structure
</pre></div>

</li><li> Structures may contain <code>UNION</code> blocks. For more detail see the
section on <a href="UNION-and-MAP.html#UNION-and-MAP">UNION and MAP</a>.

</li><li> Structures support old-style initialization of components, like
those described in <a href="Old_002dstyle-variable-initialization.html#Old_002dstyle-variable-initialization">Old-style variable initialization</a>. For array
initializers, an initializer may contain a repeat specification of the form
<code>&lt;literal-integer&gt; * &lt;constant-initializer&gt;</code>. The value of the integer
indicates the number of times to repeat the constant initializer when expanding
the initializer list.
</li></ul>

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Next: <a href="UNION-and-MAP.html#UNION-and-MAP" accesskey="n" rel="next">UNION and MAP</a>, Previous: <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" accesskey="p" rel="prev">Read/Write after EOF marker</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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